N73188 – Cessna (Textron Aviation) 207A – 1999-04-14 NTSB Accident Report

HISTORY OF FLIGHT

On April 14, 1999, about 0930 Alaska daylight time, a Cessna 207A airplane, N73188, was destroyed after crashing on an ice and snow-covered lagoon, about 10.3 nautical miles east of Kotzebue, Alaska. The airplane was being operated as a visual flight rules (VFR) scheduled domestic flight under Title 14, CFR Part 135, when the accident occurred. The airplane was operated as Flight 303X, by Village Aviation Inc., doing business as Camai Air. The flight was an extra section to scheduled Flight 303. The certificated airline transport pilot, the sole occupant, received fatal injuries. Instrument meteorological conditions prevailed in the area of the accident. A VFR flight plan was filed.

At 0845:44, the pilot contacted the In-Flight One position of the Kotzebue Flight Service Station (FSS) on a frequency of 122.2 MHz. The pilot filed a VFR flight plan to Noorvik, Alaska, with a return to Kotzebue. His planned time en route was one hour, and he said he had three hours of fuel. The pilot departed with cargo consisting of U.S. mail, and opened his flight plan at 0847:19. The distance from Kotzebue to Noorvik is 37 nautical miles, and the operator said the flight usually takes 28 minutes. The weather conditions at Kotzebue included a visibility of 3 miles in light snow and mist.

After the flight departed Kotzebue, the weather conditions deteriorated below basic VFR minimums. At 0908, a special weather observation at Kotzebue included a visibility of 1.5 miles in light snow and mist.

At an estimated time of 0920, the airplane departed the Robert Curtis Memorial Airport, Noorvik, Alaska, with no mail or cargo for the return flight to Kotzebue. There are no weather reporting facilities at Noorvik. Instrument meteorological conditions prevailed at Kotzebue as the accident flight was returning from Noorvik. Special VFR (SVFR) clearances, upon request of pilots, were being granted by Kotzebue FSS personnel for operations in the Class E airspace around the Kotzebue airport.

At 0928:48, Kotzebue FSS personnel and other pilots monitoring the Kotzebue common traffic advisory frequency (CTAF) of 123.6 MHz, heard a radio call of "mayday, mayday, mayday." The pilot's voice was identified by those hearing the radio call. At 0933:48, aircraft in the area reported hearing an emergency locator transmitter (ELT) signal. The ELT was not heard at the Kotzebue FSS.

Ground search personnel departed Kotzebue on snow machines, and located the wreckage on the Hotham Inlet, about 1055. The accident site is about 1/2 nautical mile east of the shoreline of the Baldwin Peninsula.

The accident occurred during the hours of daylight at latitude 66 degrees, 50.908 minutes north, and longitude 162 degrees, 09.965 minutes west.

CREW INFORMATION

The pilot held an airline transport pilot certificate with airplane single-engine land, single engine sea, multiengine land, and multiengine sea ratings. He also held commercial pilot privileges with a rotorcraft helicopter rating. The most recent second-class medical certificate was issued to the pilot on April 6, 1998, and contained the limitation that the pilot must have available glasses for near vision.

No personal flight records were located for the pilot, and the aeronautical experience listed on page 3 of this report was obtained from the operator's records. The pilot was hired on August 14, 1998. Prior to joining the company, he accrued extensive 14 CFR Part 135 experience flying in Alaska,.

The pilot completed an airman competency/proficiency check flight under Title 14 CFR Part 135.293 (Initial and Recurrent Testing), and 135.299 (Pilot-in-Command Line Check), with the chief pilot for the operator in a Cessna 207 airplane on August 21, 1998. A CFR Part 135.299 (Instrument Proficiency Check) check flight was not performed, nor was it required. The chief pilot noted that the pilot demonstrated basic IFR competency.

According to company records, the pilot's total aeronautical experience exceeded 10,000 hours, of which over 7,800 hours were accrued in the accident airplane make and model. In the preceding 90 and 30 days prior to the accident, the company listed a total of 175 and 66 hours respectively. The accident flight was the pilot's first flight since he last flew on April 10, 1999.

AIRCRAFT INFORMATION

An annual inspection of the airframe and engine had been completed the day before the accident. At that time, the airplane had accumulated a total time in service of 16,789.2 hours. The airplane then flew an additional .7 hours before the accident. During the annual inspection, the right wing fuel tank was drained of about 30 gallons of fuel to replace a fuel line.

The engine was rebuilt by the Teledyne Continental Motor Company on October 15, 1997. It was installed on the accident airplane by the operator on February 13, 1998. At the time of the annual inspection on April 13, 1999, the engine had accrued 1,179.2 hours since it was rebuilt. It then accrued an additional .7 hours before the accident.

The airplane is equipped with two fuel tanks, one mounted in each wing. Each tank has a capacity of 40 gallons, with 3.5 gallons as unusable fuel. Fuel cannot be used from both tanks simultaneously.

The station manager reported the pilot did not place any fuel into the right wing fuel tank of the airplane before departure to Noorvik. The left wing fuel tank contained an estimated 30 gallons of fuel.

The airplane was equipped with basic instruments for flight in instrument conditions.

The engine was equipped with a dry air pump that provided suction power for the airplane's attitude indicator, and the directional indicator. An Airborne dry pump, overhauled by Rapco Inc., was installed on the engine by the operator on October 19, 1998. At the time of the accident, the pump had accrued 634.0 hours. During the annual inspection on the day before the accident, the operator's inspection run-up sheet contained a notation that the vacuum pressure was 5.1 inches. The normal suction range is between 4.6 and 5.4 inHg.

In the event of a loss of suction from the engine driven vacuum pump, the airplane was equipped with a redundant, standby vacuum system from Precise Flight Inc., Bend, Oregon. The system was installed on March 2, 1990, under Supplemental Type Certificate (STC) number SA216NM. The system consisted of a valve installed in a hose between the engine intake manifold, and the airplane's attitude instruments. A cable was installed between the valve and the instrument panel. The valve was rotated to the open position by pulling on an instrument panel knob. An "instrument source/pump inop warning" light emitting diode (LED) was also installed in the instrument panel to alert the pilot of a primary vacuum system failure.

METEOROLOGICAL INFORMATION

The closest official weather observation station is located at Kotzebue. Instrument meteorological conditions existed at the airport as the pilot was returning from Noorvik. At 0908, a special weather observation was reporting in part: Wind, 030 degrees (true) at 7 knots; visibility, 1.5 statute miles in light snow and mist; clouds and sky condition, 2,100 feet scattered, 3,600 feet overcast; temperature, 12 degrees F; dew point, 8 degrees F; altimeter, 30.10 inHg.

Search personnel at the accident scene reported overcast clouds and fog. Flat lighting conditions prevailed with little definition or contrast between the horizon and the ground.

COMMUNICATIONS

Review of the air-ground radio communications tapes maintained by the FAA at the Kotzebue FSS facility, revealed the pilot communicated with the position of In-Flight One when he filed a VFR flight plan. The FAA found no record indicating the pilot received a weather briefing. A transcript of the air to ground communications between the airplane and the Kotzebue FSS is included in this report.

Continuous data recording (CDR) radar data from the Kotzebue Air Route Traffic Control Center radar site was reviewed by National Transportation Safety Board investigators to determine the flight track of the accident airplane. A radar track from an aircraft with a VFR transponder code of 1200, was located beginning at 0921:29, about 10.4 miles west of Noorvik. The radar track continued in a westerly direction. The radar track stopped at 0929:29, about 1.2 miles west of the accident scene.

The last radar return, and the accident location, lie within the Kotzebue Airport Class E airspace.

A copy of the radar data is included in this report.

AERODROME AND GROUND FACILITIES

The Ralph Wien Memorial Airport at Kotzebue is equipped with a hard-surfaced runway on a 080 to 260 degree magnetic orientation. Runway 26 is 5,900 feet long by 150 feet wide, and is equipped with high intensity runway lights, runway end identifier lights, and a visual slope indicator system. A second gravel runway, located south of runway 26, is oriented on a 170 to 350 degree magnetic orientation. Runway 17 is 3,896 feet long by 90 feet wide, and is equipped with medium intensity runway lights. The airport is served by both precision and nonprecision instrument approach procedures.

The airport lies within Class E airspace. The eastern edge of the airspace is located about 11 miles east of the Kotzebue airport.

WRECKAGE AND IMPACT INFORMATION

The National Transportation Safety Board investigator-in-charge (IIC), an FAA airworthiness inspector from the Fairbanks Flight Standards District Office, and an Alaska state trooper, went to the accident site on April 15, 1999. The trooper said about 4 inches of snow had fallen at the wreckage site since the accident. A depression in the snow, followed by a path of wreckage debris to the wreckage point of rest, was observed on a magnetic heading of 037 degrees. (All heading/bearings noted in this report are oriented in relation to magnetic north.)

The first observed point of impact was a semi-circular depression in the snow, about three feet wide and eight feet long. Two smaller impressions were observed on either side of the main depression. The first portion of the airplane located along the wreckage path was the right side fuselage step, about 30 feet beyond the first observed point of impact. About 20 feet beyond the step was the nose wheel vibration dampner. Additional portions of the airplane were found along the wreckage path, and included, in the order observed: windshield fragments, wing lift strut fairing fragments, the upper engine cowling, the right wing tip fairing, the right front cabin door, the nose wheel strut, portions of instrument panel, the forward section of the right side cargo door, the left front cabin door, fragments of the engine mount, nose cargo door and nose wheel, and portions of the nose/engine keel structure.

The directional gyro, the attitude gyro, the turn coordinator, the altimeter, and the vertical speed indicator, were broken out of the instrument panel.

The main fuselage wreckage came to rest about 300 feet from the first observed point of impact. The airplane was lying inverted with the left wing lying flat along the surface of the snow. The left wing was positioned about 45 degrees aft of its normal position. The wing spar carry-through was torn from the fuselage. The lift strut was attached to the wing, but separated from the fuselage. The left wing displayed spanwise aft, vertical/flat crushing, of the leading edge from the pitot tube to the outboard edge of the flap. Forty-five degree aft flat crushing and folding of the leading edge was evident from the flap to the tip.

The wing tip was attached to the wing, along with the position light and strobe. Examination of the left wing position bulb filament revealed the filament was broken about mid-span. The visible portion of the filament was tightly coiled. The aileron was attached to the wing, but buckled in a U-shape, with aft crushing and upward curling of the trailing edge. The flap remained attached to the wing. Fuel was found in the left wing fuel tank.

The right wing was fractured at the inboard end and was standing vertically with the wing tip up, with the leading edge oriented 90 degrees to the fuselage in an inboard direction. The leading edge had extensive spanwise leading edge aft and upward crushing and buckling along a 45 degree angle from the trailing edge of the wing tip, to about the inboard end of the aileron attach point. The aileron and flap remained attached to the wing. The lift-strut was attached to the wing. The lift-strut was attached to the fuselage at its lower attach point, but had a 120 degree U-shaped bend, about one foot from the fuselage.

An area of oil residue was found splattered on the leading edge of the right wing, and along the upper and lower surface, about the lift-strut attach point. Evidence of oil streaking was not found on the belly of the fuselage, the windshield or upper surface of the fuselage, the empennage, the inside of the engine cowling, or on the firewall.

The upper left corner of the fuselage was crushed in a downward direction, almost to the bottom of the windshield. The cabin area, aft of the trailing edge of the wing was buckled and distorted. The aft section of the right side cargo door remained attached to the fuselage.

The empennage, just forward of the vertical stabilizer attach point, was twisted and buckled to the left. Both horizontal stabilizers were free of any major damage. The vertical stabilizer was curled to the left at its aft, upper edge. The rudder was curled to the left near the top. The elevator and trim tab remained attached to the horizontal stabilizer and was free of any major damage. Examination of the rear fuselage position bulb filament revealed the filament was intact and tightly coiled.

The flap jackscrew actuator was extended about 3/4 inch. According to the airplane manufacturer, the flap jackscrew extension corresponded to a near zero flap condition. The elevator trim tab actuator was found extended about 2 1/4 inches. The trim tab actuator corresponded to about a 25 degree tab up (nose down) setting. The normal range of trim tab extension is from 25 degrees tab up, to 5 degrees tab down.

The main landing gear remained attached to the fuselage. The right main gear strut was displaced aft. The forward face of the right main landing gear strut fairing had aft vertical/flat crushing. The inboard area of the forward face of the left main landing gear strut fairing had similar aft flat crushing.

The fuselage, forward of the front door posts and including the instrument panel, firewall, and nose baggage area, was buckled, crushed, and torn in a downward direction. The bottom portion of the fuselage skin, just aft of the nose wheel well had a black smudge. Due to impact damage, the flight controls could not be moved by their respective control mechanisms.

Fuel was contained in the fuselage gascolator. The gascolator screen had several specks of contaminants. The fuel selector was on the left tank.

The propeller hub assembly separated from the engine crankshaft about 2 inches inboard from the propeller flange. The propeller was located about 250 feet from the initial observed point of impact. The fracture surface of the propeller/crankshaft had multiple, 45 degree angled shear faces.

All three propeller blades were retained in the hub, but were loose and rotated within the hub. One propeller blade had about 90 degree aft bending and aft curling at the tip. The leading edge had file marks, a gouge about 10 inches inboard from the tip, but was generally free of damage. Minor paint removal was evident about 8 inches inboard from the tip, and minor scuffing along the upper surface of the blade. The second blade displayed leading edge file marks, slight aft bending, and slight aft curling at the tip. Spanwise scuffing and scratching was observed about two inches inboard from the tip. The third blade had an aft 90 degree bend, about 8 inches inboard from the tip. The blade had slight torsional twisting, and minor scuffing at the tip. The leading edge had file marks, but no chordwise scratching or gouging.

The engine separated from the fuselage, and was lying inverted about 15 feet from the fuselage, and about 275 feet from the initial observed point of impact. It sustained impact damage to the underside, and front portion of the engine oil sump. Upon turning the engine over, frozen impressions in the snow were found that matched the cooling fin pattern of the forward engine cylinders. The exhaust tubes had minor bending and denting without sharp creases. The muffler tube extensions were crushed and flattened. The creases and folds of the metal were not cracked or broken.

The fuel manifold contained fuel, without any evidence of contamination in the manifold screen. The fuel servo inlet screen was free of contaminants.

The engine breather/crankcase ventilation tube separated from the case. It was distorted and broken. The interior of the vent tube contained black grease deposits. The movement of air through the tube was demonstrated.

After the wreckage was recovered from the ice, the NTSB IIC and an FAA inspector reexamined the wreckage on April 26, 1999, in Kotzebue. During the examination, the interior of the left wing was examined to document the flight control cable continuity. Portions of shattered, bright orange plastic were found within the wing structure. The metal shaft portion of a combination screw driver was also found within the wing, about mid-chord/mid-span, resting against a small vertical portion of wing structure. The location was inboard from the aileron cable pulley. The recovered plastic pieces appeared to be the handle portion of the combination screw driver. Recovery personnel stated the airplane wreckage was secured to sleds that were pulled behind snow machines about 15 miles over rough areas of snow. The left wing had numerous areas of open and crushed structure, and was not completely intact.

Examination of the left wing aileron cable, and aileron pulley discovered no area of impingement.

Flight control system cable continuity was established to the point of impact-related damage.

The standby vacuum system knob, installed at the bottom edge of the pilot's side instrument panel area, was not extended from the face of the instrument panel. The panel was extensively bent and distorted.

MEDICAL AND PATHOLOGICAL INFORMATION

A postmortem examination of the pilot was conducted under the authority of the Alaska State Medical Examiner, 5700 E. Tudor, Anchorage, Alaska, on April 15, 1999. The pilot sustained extensive injuries to the right side of his chest.

TESTS AND RESEARCH

On April 28, 1999, an external engine examination was conducted at Alaskan Aircraft Engines, Anchorage, Alaska.

The engine case was broken along the lower, forward edge of engine sump. The oil sump was crushed upward against the case at the forward end. The crushing of the sump angled aft and downward on a 45 degree angle to the rear of the sump where almost no damage was evident.

Gear and valve train continuity was established.

The engine propeller nose seal, located in the forward end of the engine case was intact within the case.

The engine driven fuel pump drive gear was intact, and the pump was free to turn by hand.

Examination of the gyro rotor and housing from the airplane's directional gyro instrument revealed the rotor, and the internal housing were undamaged.

The engine vacuum pump housing was broken at its forward mounting flange. The vacuum pump's plastic drive gear had partial circumferential tearing around its design shear point. Examination of the internal vacuum pump block revealed it was shattered. The pump vanes were not broken or chipped. The support post for the block was sheared at the base of its attach point to the outer half of the pump housing. Visual examination of both fracture surfaces of the support post did not reveal smearing, battering, or deformation of the fracture features.

Examination of the pump support shaft by the Safety Board's Materials Laboratory revealed ratchet marks and fracture features consistent with fatigue progression through an estimated 70 percent of the shaft cross section. The remaining area of separation was consistent with an overstress fracture. Numerous areas of fatigue origins were noted in the fillet radius between the cylindrical shaft and the sealing face of the pump's end cap.

The valve portion of the standby vacuum system was found in the closed position. The control cable from the cockpit to the valve was not attached.

The intake tube assembly, located along the left side of the engine that supplied intake air to the number two, four, and six cylinders, was shattered along its lower circumference. The forward portion of the number four induction tube, where it is normally inserted into a rubber sleeve between the number four and six cylinder, had a longitudinal fracture along the upper circumference of the tube. The fracture appeared to be located along the manufacturer's casting line. Examination of the fracture surface by the Safety Board's Materials Laboratory revealed fracture features typical of an overstress separation with no indication of preexisting cracking.

Removal of the engine cylinders revealed small pieces of shattered intake tube in the combustion chamber of the number six and number four cylinders. The top of the number six piston displayed small nicks. The top of the number four piston was undamaged.

The surface of the combination screw driver found in the left wing was examined by the Safety Board's Materials Laboratory for contact marks from the wing flight control components. None were found.

A sound spectrum study of the audio recording of the pilot's radio calls, provided by the Kotzebue FSS, was examined by the Safety Board's Vehicle Recorder Division. Recording noise from the FSS equipment associated with a 60 Hz signal, and corresponding harmonics, was present on the audio recording. During the pilot's radio call to open his flight plan, harmonic signal data was found that equated to about 2,466 to 2,493 RPM, but the data could not be confirmed as belonging to engine noise. During the pilot's "mayday" call, harmonic signal data was found that equated to about 2,200 RPM, but the data could not be confirmed as engine sounds. Due to insufficient signal data, over a long enough period of time, the sound spectrum study was inconclusive to determine if engine sounds were present during the pilot's "mayday" call.

WRECKAGE RELEASE

The Safety Board released the wreckage, located at Kotzebue, Alaska, to the owner's representatives on May 27, 1999. The vacuum pump support shaft, and the induction tube was retained by the Safety Board for examination until its release on August 12, 1999.